Liard Basin – Middle Devonian Exploration
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LIARD BASIN – MIDDLE DEVONIAN EXPLORATION Warren Walsh1, Osman Salad Hersi2, Mark Hayes1 ABSTRACT The Liard Basin is a sub-basin of the Western Canada Sedimentary Basin (WCSB) system, straddling the Northwest and Yukon Territories boundary with the Province of British Columbia. The basin contains over 5 km of sedimentary strata of Cambrian through Upper Cretaceous age. Exploration for Manetoe Dolomite reservoirs hosted within middle Devonian carbonates of the Dunedin and Nahanni formations began in the 1950’s. Several pools have been found within the fold and thrust belt both in Northeastern British Columbia and the Yukon and Northwest Territories. Recent gas discoveries within the Devonian Nahanni Formation north of Fort Liard, NWT has renewed interest in this play. Resource assessments for the middle Devonian play in the Liard Basin estimates between 2.8 and 6.6 Tcf undiscovered gas, with approximately 2.5 Tcf estimated to be located within Northeastern British Columbia. The British Columbia Ministry of Energy and Mines (BC MEM) is currently working with the University of Regina and the Geological Survey of Canada (GSC) to expand our knowledge and understanding of the Liard Basin. Through a contribution agreement, the BC MEM, in conjunction with Dr. Osman Salad Hersi of the University of Regina, is supporting graduate level studies on the sedimentology, stratigraphy and diagenesis of Middle Devonian, shallow-marine carbonates of the Dunedin Formation of subsurface Liard Basin, with application to petroleum exploration. The BC MEM also continues their relationship with the GSC, who has recently published a reinterpretation of the Bovie Structure which included the identification of new conceptual plays within the Liard Basin. Warren Walsh, Osman Salad Hersi, Mark Hayes, Liard Basin – Middle Devonian Exploration in Summary of Activities 2005, BC Ministry of Energy and Mines, pages 38-41. 1Resource Development and Geoscience Branch, BC Ministry of Energy and Mines, PO Box 9323, Victoria BC, V8W 9N3 2Department of Geology, University of Regina, Regina, SK, S4S 0A2 Keywords: Northeastern British Columbia, Liard Basin, Dunedin Formation, Manetoe Dolomite Facie Devonian, Carboniferous and Cretaceous strata associated with the Bovie Fault (MacLean and Morrow, 2004). INTRODUCTION The western side of the Liard Basin is referred to as the Liard Plateau or the Liard Fold and Thrust Belt, a The Liard Basin is a sub-basin of the extensive northward continuation of the fold and thrust belt of the Western Canada Sedimentary Basin (WCSB) system, Rocky Mountain foothills. Within this area, several straddling the Northwest and Yukon Territories boundary hydrocarbon pools have been discovered within with the Province of British Columbia. The basin covers a carbonates of the middle Devonian and several gas shows total area of approximately 2.5 million hectares with up to have been found at Mississippian through Permian 5000 m of Paleozoic and Mesozoic sedimentary fill. The intervals. The middle Devonian carbonate play type has Liard Basin is a frontier basin whose hydrocarbon upwards of 2.35 Tcf of remaining undiscovered gas in potential is only just beginning to be appreciated. place within Northeastern British Columbia (NEB, 2000). The eastern boundary of the Liard basin is delineated The stratigraphy, sedimentology and diagenetic history of by the Bovie Fault System, which also marks the the middle Devonian Dunedin Formation of British approximate eastern limit of Mississippian through Upper Columbia is the focus of a multi-year collaboration Cretaceous strata (Monahan, 2000). Recent work by the between the University of Regina and the BC MEM. Geological Survey of Canada (GSC), supported by the A geological map of the Liard Basin has been created British Columbia Ministry of Energy and Mines (BC and is now available to aid exploration. The 1:250 000 MEM) has reinterpreted the nature and history of the scale map is a compilation of geology maps separately Bovie Structure (MacLean, 2002; MacLean and Morrow, issued by the Geological Survey of Canada and has been 2004). MacLean and Morrow (2004) have reinterpreted updated with infrastructure, land tenure and petroleum the Bovie Fault as a two-stage compression; (i) a late- and natural gas wells for the entire Liard Basin. Carboniferous to Permian westward convergent steeply Production data and Drill Stem Test results and dipping thrust fault, which is cut by (ii) the Larimide aged interpretation for the middle Devonian have also been Bovie Lake Thrust. This reinterpretation of the Bovie summarized. Structure has also identified several potential play types in Summary of Activities 2005 38. GEOLOGIC SETTING, Lake, 1989, Morrow and Davies, 2001). The dolomitized strata are known as the Manetoe Dolomite Facies PALEOGEOGRAPHY, AND (Manetoe) in the Northwest and Yukon territories STRATIGRAPHY (Morrow and Potter, 1998; Morrow et al. 1986, 1990); they form good reservoir intervals in many gas-producing fields in the region (e.g., Pointed Mountain, Kotaneelee, Dunedin Formation Fort Liard, Beaver River and Crow River gas fields). The Manetoe is characterized by a fractured and brecciated In the Devonian Period, NE BC and nearby regions white sparry dolomite (Morrow et al. 1990; Morrow and of Alberta, Yukon and Northwest Territories were cut by Potter, 1998). Although the Manetoe dolomite facies that several rifting events that produced deep depressions and occur within the Dunedin and Nahanni-Landry uplifted shoulders that later became shallow marine shelf successions of Yukon and NWT, respectively are fairly areas (Cecile et al. 1997, Pyle et al. 2003). The well documented (Morrow and Potter, 1998; Morrow and Macdonald-Mackenzie shelf was the most prominent in Davies, 2001, Morrow et al. 1986, 1990), knowledge is northeastern British Columbia and nearby regions, lacking in NE BC, as the equivalent dolomites of the allowing deposition of thick carbonate successions that Dunedin Formation are relatively less understood. include the largest carbonate reservoirs in the region Understanding the origin, fabric, porosity, reservoir (Moore, 1989, Pyle et al. 2003). potential and vertical and lateral distributions of this The Dunedin Formation consists of Middle Devonian dolomite facies is essential for gas exploration activities (Eifelian) carbonate strata that were deposited on the within this prospective frontier basin. MacDonald Shelf. The shelf continued across the B.C.’s border with the Yukon and Northwest territories where equivalent strata, the Landry-Nahanni formations, were MIDDLE DEVONIAN HYDROCARBON deposited. Southward (i.e., Southern NE BC and NW Alberta), the Dunedin Formation merges with the prolific POTENTIAL Keg River Formation (Nadjiwon, 2001). These middle Devonian carbonates contain hydrothermally dolomitized facies (Manetoe dolomite facies and equivalents; see Fold and Thrust Belt below) with potentially good reservoir quality. Exploration to date for middle Devonian Manetoe The Dunedin Formation is a transgressive unit Dolomite within the Dunedin and Nahanni formations has dominated by peritidal and subtidal shallow marine been focused within the Liard Fold and Thrust Belt. The carbonates and, due to southward facies retrogradation, Liard fold and thrust belt of BC covers an area of the Besa River Formation oversteps the Dunedin approximately 1.25 million hectares. Exploration has Formation in the southeastern (Morrow, 1978, Nadjiwon, resulted in the discovery of two fields, Beaver River and 2001). Broad subdivision of the Dunedin Formation Crow River. Outside of these two fields, only 6 documents that the formation consists of a lower exploration wells have been drilled targeting the middle lithofacies characterized by a bioclastic dolomitic Devonian, all drilled prior to 1974. Within the Yukon and wackestone and an upper lithofacies of a bioclastic NWT, a total of 5 middle Devonian fields have been grainstone to wackestone units (Morrow, 1978, Nadjiwon, discovered with less than 10 exploration wells outside of 2001). Further south, where the formation passes to the proven fields. reefal Keg River Formation, intercalations of coral and Exploration within the Liard basin began in the stromatoporoid reef facies are common. Due to the reefal 1950’s with the first well drilled in the Liard Fold belt at “tongues”, the thickness of the Dunedin Formation varies the Toad River Anticline (Joint Venture No. 1 c-10-E/94- significantly (e.g., from 108 m to over 300 m within a N-7; rig released in 1954). Amoco Canada Petroleum Co. distance of 11 km, Nadjiwon et al., 2000), however, Ltd. made the first discovery at the Beaver River Field in causes of this abrupt thickness change are not clear. 1958. Further drilling delineating the Beaver River pool Possibilities may include synsedimentary faulting and/or and subsequent discoveries were made in the 1960’s at establishment of reefal margin defined by differential reef Pointed Mountain in the North West Territories and growth responses to sea level fluctuations (cf. Kotaneelee, Yukon Territory. Originally over 1.4 Tcf of transgression-instigated catch-up situation of Jones and reserves were associated with the Beaver River pool Desrochers, 1992). The Dunedin Formation continues alone, however, high water to gas ratios resulting from the across the northern provincial-territorial borders where it highly fractured reservoir and active water drive led to is equivalent with the gas-producing Landry-Nahanni lower than expected recoveries from these